Comparison of Measured and Modeled Turbulence Spectra for a Point Rotating as on a Horizontal-Axis Wind Turbine

Abstract

A theoretical model of the spectrum of rotationally sampled wind speed is tested against corresponding measured wind spectra. The ability to generate such a spectrum, independent of measurement, is important in wind turbine design and testing. The measured spectra were selected from a number of cases measured with a vertical plane array of anemometers. The array was set up to correspond to the tip circle of a nearby MOD-OA wind turbine rotor blade. For testing purposes, the turbulence and mean wind shear were treated separately. In each case the test was based on two correspondence criteria, each involving comparison of results from the theoretical model and results from real data analysis. These criteria were rotational spectra and their integration by harmonic band into energy, particularly the latter. The measured spectra were selected to represent different atmospheric stability conditions. The theory is shown to have respectable accuracy except when applied to the stable atmosphere. Recommendations were made for selection of the values of atmospheric parameters to be used for computing the theoretical result. The importance of the time length of a measured turbulence record to be used in estimating several parameters for input to the theoretical model applied to real wind conditions at a selected turbine site is discussed. The VAX 11/780 computer time required to generate a model spectrum is usually less than one minute.